Characterization of virtual coupling in the proton nuclear magnetic resonance spectrum of N,N'-diacetylchitobiose by two-dimensional J-resolved spectroscopy.

The anomeric proton of the reducing N-acetylglucosamine residue of beta-N,N'-diacetylchitobiose exhibited an unusual lineshape indicative of virtual coupling in the 250 MHz proton NMR spectrum. The two-dimensional J-resolved spectrum contained four lines associated with this proton, and this pattern can be used to distinguish virtual coupling from other effects. Anomeric protons of previously studied asparagine-linked glycopeptides which exhibited unusual lineshapes in the conventional NMR spectra did not exhibit the four line patterns indicative of virtual coupling in the two-dimensional J-resolved spectra. Although virtual coupling may partially account for the unusual lineshapes observed in the normal proton NMR spectra, the anomalous behavior observed in the two-dimensional J-resolved spectra of these glycopeptides cannot be explained solely by this phenomenon.